1. Field of the Invention
The present invention relates generally to a system and method for measuring corrosion, and more particularly relates to a system and method for detecting localized corrosion in vessels, piping, valves, pumps, and other equipment exposed to a corrosive environment based on the time required for corrosion to proceed through a predetermined thickness of corrosion sensor material.
2. Description of Related Art
Reliable corrosion monitoring of various process equipment is extremely important. For example, it is generally known that various industrial processes produce corrosive by-products. Such corrosive by-products frequently corrode industrial equipment, increase production costs, and create production delays. Thus, corrosion monitoring is a valuable tool which can alleviate such process upsets. Various attempts have been made using electrochemical (EC) and non-electrochemical techniques to identify corrosion processes. For example, linear polarization resistance (LPR) and electrochemical noise methods have been used to identify corrosion rates, types of corrosion, and parameters associated with localized corrosion. Other techniques include the application of electrical resistance (ER) measurements to determine loss of thickness and hence determine corrosion rates. Foil penetration methods have also been used to study the kinetics of pitting in aluminum and aluminum alloys. However, these methods have not been entirely satisfactory in providing an unambiguous method to determine the propagation of localized corrosion in a robust and cost effective manner.
One of the problems encountered with currently available corrosion monitoring methods and devices is that none of the methods provide reliable and unambiguous measures of the uniform corrosion rate or the rate of localized corrosion. The LPR technique typically only provides information on uniform corrosion conditions because it provides an average signal for the surface of the electrode being monitored. Depending upon the environment, metallic material, and corrosion type, the assumption that the corrosion rate is proportional to the measured charge transfer or polarization resistance is invalid when the corrosion is of a localized nature. It is known that localized corrosion (e.g. pitting) is a leading cause of system failure. With LPR, the instantaneous corrosion rate may vary by several orders of magnitude over a short time, and thus, the computed rate may or may not by itself produce much meaningful information. Moreover, due to the complex nature of the measurements and varying resistances involved, the rate at which the potential is scanned may have a significant effect on the amount of current produced at all values of potential sign. Such systems require precise measurements of small incremental changes in the electrical properties of the sensor device, thus making them quite susceptible to noise. Accordingly, such devices typically require relatively complex and expensive components, substantially increasing the cost of making and using such devices. A drawback of ER-type sensors is their considerable bulk due to the long length of the exposed strip necessary to make changes in resistance easily measurable. Although it may be possible to reduce the thickness of the strip, this will adversely impact sensor life because a reduced sensor thickness will corrode entirely through in a shorter period of time.
In view of these limitations, it would be desirable to provide a sensor system and method which is relatively simple and cost effective to manufacture and use, which is substantially robust to noise, and which is capable of measuring localized corrosion (i.e., pitting) with cumulative corrosion measurements.